diff --git a/src/main/java/ch/unibas/dmi/dbis/cs108/casono/client/chat/ChatController.java b/src/main/java/ch/unibas/dmi/dbis/cs108/casono/client/chat/ChatController.java
index 6c30307..d3ac3c0 100644
--- a/src/main/java/ch/unibas/dmi/dbis/cs108/casono/client/chat/ChatController.java
+++ b/src/main/java/ch/unibas/dmi/dbis/cs108/casono/client/chat/ChatController.java
@@ -9,6 +9,7 @@ import java.util.List;
 import java.util.Map;
 import java.util.Timer;
 import java.util.TimerTask;
+import java.util.WeakHashMap;
 import org.apache.logging.log4j.LogManager;
 import org.apache.logging.log4j.Logger;
 import org.jspecify.annotations.Nullable;
@@ -19,8 +20,14 @@ import org.jspecify.annotations.Nullable;
  */
 public class ChatController {
 
+    /** Ensures one active message poller per physical ClientService connection. */
+    private static final Map<ClientService, ChatController> ACTIVE_CONTROLLERS =
+            new WeakHashMap<>();
+
     private final String username;
 
+    private final ClientService clientService;
+
     private final ChatClient chatClient;
 
     public ChatBoxController getChatBoxController() {
@@ -58,11 +65,15 @@ public class ChatController {
      */
     public ChatController(String username, ClientService clientService) {
         this.username = username;
+        this.clientService = clientService;
         chatClient = new ChatClient(clientService);
         chatModelMap = new LinkedHashMap<>();
         localUserList = new ArrayList<>();
         this.chatBoxController = new ChatBoxController(username, this);
         this.logger = LogManager.getLogger(ChatController.class);
+
+        registerAsActiveController(clientService);
+
         this.timer = new Timer(true);
         timer.schedule(
                 new TimerTask() {
@@ -80,6 +91,17 @@ public class ChatController {
                 REFRESH_TIME);
     }
 
+    private void registerAsActiveController(ClientService clientService) {
+        synchronized (ACTIVE_CONTROLLERS) {
+            ChatController oldController = ACTIVE_CONTROLLERS.get(clientService);
+            if (oldController != null && oldController != this) {
+                oldController.shutdown();
+                logger.info("Replaced previous ChatController poller for shared ClientService");
+            }
+            ACTIVE_CONTROLLERS.put(clientService, this);
+        }
+    }
+
     /**
      * Method to be activated, if a lobby has been chosen. It will update the UI and add a new
      * ChatModel to hold the Data for the Lobby Chat
@@ -158,8 +180,8 @@ public class ChatController {
     }
 
     /**
-     * Method to get the lobbyId of the currently active lobby chat, to check if incoming lobby messages
-     * belong to the same lobby.
+     * Method to get the lobbyId of the currently active lobby chat, to check if incoming lobby
+     * messages belong to the same lobby.
      *
      * @return the lobbyId of the currently active lobby chat.
      */
@@ -210,6 +232,11 @@ public class ChatController {
     /** Stops polling background tasks for this chat controller instance. */
     public void shutdown() {
         timer.cancel();
+        synchronized (ACTIVE_CONTROLLERS) {
+            if (ACTIVE_CONTROLLERS.get(clientService) == this) {
+                ACTIVE_CONTROLLERS.remove(clientService);
+            }
+        }
     }
 
     /**
diff --git a/src/main/java/ch/unibas/dmi/dbis/cs108/casono/server/app/commands/send_message/SendMessageHandler.java b/src/main/java/ch/unibas/dmi/dbis/cs108/casono/server/app/commands/send_message/SendMessageHandler.java
index 94ee193..a2bd3ad 100644
--- a/src/main/java/ch/unibas/dmi/dbis/cs108/casono/server/app/commands/send_message/SendMessageHandler.java
+++ b/src/main/java/ch/unibas/dmi/dbis/cs108/casono/server/app/commands/send_message/SendMessageHandler.java
@@ -1,7 +1,8 @@
 package ch.unibas.dmi.dbis.cs108.casono.server.app.commands.send_message;
 
-import ch.unibas.dmi.dbis.cs108.casono.client.chat.Message;
 import ch.unibas.dmi.dbis.cs108.casono.client.chat.ChatType;
+import ch.unibas.dmi.dbis.cs108.casono.client.chat.Message;
+import ch.unibas.dmi.dbis.cs108.casono.server.domain.lobby.Lobby;
 import ch.unibas.dmi.dbis.cs108.casono.server.domain.lobby.LobbyId;
 import ch.unibas.dmi.dbis.cs108.casono.server.domain.lobby.LobbyManager;
 import ch.unibas.dmi.dbis.cs108.casono.server.domain.user.UserRegistry;
@@ -38,7 +39,7 @@ public class SendMessageHandler extends CommandHandler<SendMessageRequest> {
     @Override
     public void execute(SendMessageRequest request) {
         Message message = request.getMessage();
-        broadcast(message);
+        broadcast(request, message);
         OkResponse response = new OkResponse(request.getContext());
         responseDispatcher.dispatch(response);
     }
@@ -49,20 +50,35 @@ public class SendMessageHandler extends CommandHandler<SendMessageRequest> {
      *
      * @param message The {@link Message} object to be broadcast.
      */
-    public void broadcast(Message message) {
-        if (message != null
-                && message.getMessageType() == ChatType.LOBBY
-                && message.lobbyId >= 0
-                && lobbyManager != null) {
-            lobbyManager.broadcast(
-                    LobbyId.of(message.lobbyId),
-                    username ->
-                            userRegistry
-                                    .getByUsername(username)
-                                    .ifPresent(user -> user.enqueueMessage(message)));
-            return;
+    public void broadcast(SendMessageRequest request, Message message) {
+        if (message != null && message.getMessageType() == ChatType.LOBBY && lobbyManager != null) {
+            LobbyId targetLobbyId = resolveLobbyIdForMessage(request, message);
+            if (targetLobbyId != null) {
+                lobbyManager.broadcast(
+                        targetLobbyId,
+                        username ->
+                                userRegistry
+                                        .getByUsername(username)
+                                        .ifPresent(user -> user.enqueueMessage(message)));
+                return;
+            }
         }
 
         userRegistry.getAllUsers().forEach(user -> user.enqueueMessage(message));
     }
+
+    private LobbyId resolveLobbyIdForMessage(SendMessageRequest request, Message message) {
+        if (message.lobbyId >= 0) {
+            LobbyId idFromMessage = LobbyId.of(message.lobbyId);
+            if (lobbyManager.getLobby(idFromMessage) != null) {
+                return idFromMessage;
+            }
+        }
+
+        return userRegistry
+                .getBySessionId(request.getContext().sessionId())
+                .map(user -> lobbyManager.getLobbyByUsername(user.getName()))
+                .map(Lobby::getId)
+                .orElse(null);
+    }
 }